This invention relates to the electroplating of cobalt and cobalt base alloys on metal substrates and is more particularly directed to an improved electrolyte therefor which will suppress or inhibit the formation of undesirable precipitates in the presence of an insoluble or passive anode.
Certain critical areas of the interior bore surfaces of gun tubes are customarily coated with a layer of chromium plating to protect against the erosion and wear encountered during the firing of projectiles therethrough. Recent investigation of other plating materials has demonstrated that even greater protection is afforded by a coating of cobalt or an alloy of cobalt and iron. However, while chromium can be successfully electroplated by techniques which utilize an insoluble or passive anode, such is not the situation in regard to the deposition of cobalt and iron since the particular chemistry involved produces insoluble oxide precipitates which not only interfere with the efficiency of the plating process but are also codeposited with the desired metals to the detriment of the mechanical and physical properties thereof. Although these difficulties can be partially avoided by the employment of an appropriate soluble anode within the gun tube, the continuous dimensional change in the diameter thereof during the depletion of the plating metal therefrom complicates the desired attainment of a deposit of uniform thickness. Consequently, the electroplating of cobalt and cobalt base alloys on the interior bore surfaces of gun tubes has heretofore been limited to those sizes in which the bore diameters thereof are 20mm or larger.
It is therefore an object of the present invention to provide an improved method for electroplating a layer of cobalt or an alloy thereof on the interior bore surfaces of metal tubes at ambient temperatures to provide a corrosion-resistant ductill coating thereon. Ambient temperatures are normally room temperatures in the vicinity of 20.degree. C.
It is another object of this invention to provide an electroplating method, as aforesaid, which will produce cobalt and cobalt-iron deposits of uniform thickness even in gun tubes with bore diameters of less than 20mm in size.
A further object of this invention is to provide an electroplating method, as aforesaid, wherein the electrolyte therefor includes an additive capable of inhibiting or suppressing the formation of the undesirable cobalt and iron oxides heretofore produced in the presence of an insoluble or passive anode.
Still another object of this invention lies in the provision of an electrolyte, as aforesaid, wherein the additive participates in the electrochemical activity occurring at both the anode and the cathode and yet is not codeposited with the electroplated metals.
These and other objects will become apparent from the following detailed description and claims.